but I did not get the proper behavior... I looked up /var/log/messages (from other machine using ssh access to my FreeBSD system) and saw proper messages Lid: Closed and Lid: Opened as I closed and opened the lid... But monitor was turned off all time, so I needed to restart system...

After that I loaded acpi_video module using kldload and repeated the same procedure described above, with same results (display has been turned of first time I closed lid, and it have not turned on as I opened it...). Then I restarted system again, and try to see what will happen when I try to run sysctl command from console... The output was:

As I understand, you want your screen to turn off when the lid is closed and back again after opening the lid?

Under root privilege:

#sysctl hw.acpi.reset_video=1

Now close the lid and open it again, the light should be back.

For permanent setting:

# echo "hw.acpi.reset_video=1" >> /etc/sysctl.conf

Yes, you have understood what I want, but setting hw.acpi.reset_video to 1 did not give any positive results, and even after putting it in sysctl.conf and rebooting system screen turning of and on did not worked...